Safety power switch locking device

ABSTRACT

A safety power switch locking device for adjustable power machinery utilizing a tool for making such adjustments, such as power machinery having manually operated chucks and wrenches for manually operating such chucks; the device comprised of a housing for mounting over the power switch of the power machine, an elongated tumbler or other actuating lever for such switch extending into the housing together with a keyed spring-biased block or the like in said housing, said block biased toward a lock position, such lock position characterized in that the key portion of said block extends into a key receiving aperture in the power switch tumbler when in the power-off position and prevents movement of the tumbler to its power-on position, the keyed block movable to an unlock position in response to insertion of the chuck wrench into the housing through an aperture specially designed to accommodate the chuck wrench.

United States Patent [54] SAFETY POWER SWITCH LOCKING DEVICE 2 Claims, 4 Drawing Figs. [52] US. Cl 200/44, 200/ 169 R [51] Int. Cl II0lh 9/28 [50] Field of Search 200/44,

[56] References Cited UNITED STATES PATENTS 2,578,317 12/1951 Pealer .1 200/169 X 2,588,565 3/1952 Pealer 200/169 A 2,597,969 5/195'2' Barton 2,666,104 1/1954 Griffin 200/6l.58

ABSTRACT: A safety power switch locking device for ad- 7 justable power machinery utilizing a tool for making such adjustments, such as power machinery having manually operated chucks and wrenches for manually operating such chucks; the device comprised of a housing for mounting over the power switch of the power machine, an elongated tumbler or other actuating lever for such switch extending into the housing together with a keyed spring-biased block or the like in said housing, said block biased toward a lock position, such lock position characterized in that the key portion of said block extends into a key receiving aperture in the power switch tumbler when in the power-off position and prevents movement of the tumbler to its power-on position, the keyed block movable to an unlock position in response to insertion of the chuck wrench into the housing through an aperture specially designed to accommodate the chuck wrench.

PAIENTEBum 12 I97! 3,612,787

INVENTORS DEN/W5 M. KEOZ/ORA DAVID E HLAVSA g ATTORNEYS SAFETY POWER SWITCH LOCKING DEVICE BACKGROUND OF THE INVENTION This invention relates to safety devices for adjustable power machinery utilizing a tool for making such adjustments, and more particularly to safety devices for adjustable power machinery such as power machinery having manually adjustable chucks utilizing chuck wrenches or the like. Still more particularly, the invention relates to safety devices of the type described which lock the power switch for such machinery in a power-off condition, such devices suited to be unlocked and the power machine switched to power-on only while the chuck wrench for such machine is employed to hold the safety device in an unlocked condition.

In a control switch of an electrically driven power machine of the type employing a rotary chuck, the jaws of the chuck are set in place by a removable manual chuck wrench inserted into the chuck head to protrude radially from the head for several inches. In this position the wrench is used to tighten or loosen the chuck head. If the wrench is left in this position when the power machine is actuated, the wrench either remains in place and damages the machinery or the wrench is forcefully thrown off the chuck head presenting a hazard to both machinery and personnel. Serious accidents have occurred in this manner. This has been an especially serious problem with novice operators and trainees, such as are found in high school shops and other training facilities.

In the past, one partial solution to the problem has been to provide a wrench rack which is coupled to a locking device which normally locks the machines power switch in a poweroff position, but which releases the switch when the wrench is placed on the wrench rack. However, the purpose of such a device is easily frustrated by permanently placing some other weighty object on the storage rack.

An additional problem has been that these and other such safety devices are designed as original equipment and not for secondary installation on conventional existing machinery. Many training facilities can afford to purchase only secondhand equipment. It is often diflicult for such facilities to locate used machinery with safety features adequate for novice operators.

SUMMARY OF THE INVENTION Generally, the invention described involves the electric power switch of a power machine of the type requiring an adjuster tool such as a chuck wrench, and where the power switch is movable from an off position to an on position in a conventional manner. The safety power switch locking device of this invention may be mounted on existing electric power switches of the type commonly employed on power machinery. The safety device has a movable member within a housing which locks the power switch in its power-off position until one end of the adjuster tool (e.g., the handle of a chuck wrench is inserted through an aperture in the housing) into the device to move the movable member to a position releasing the power switch so that it may be turned to its power-on position. Once the power switch has been returned to the poweroff position and the adjuster tool removed, the power switch may not be turned again to a poweron position until the tool has been returned to the housing.

The locking device may not be unlocked with any other object unless it has similar dimensions to those of the adjuster tool so that it is generally more convenient for the operator to use the adjuster tool to unlock the device than to locate and use another suitable object.

In addition, the locking device is adapted for mounting directly on an existing power switch, the tumbler of that switch extending into the housing of the locking device and coupling directly with the components of the locking device so that it is easily installed as secondary equipment on used machinery of varied design.

Accordingly, it is an object of the present invention to provide a safety power switch locking device for locking the power switch of adjustable power machinery in its power-off position and which is unlocked and held open with the adjuster tool for such machinery thereby assuring that the tool has been removed from the machine prior to its operation.

Another object of the invention is to provide a safety power switch locking device for locking adjustable power machinery in a power-off condition which is unlocked and held open with the adjuster tool for such machinery and which is inconvenient or impossible to unlock and/or hold open with any other object.

A further object of the present invention is to provide a safety power switch locking device for power machinery which is conveniently installed as secondary equipment upon existing conventional power machinery.

Other objects of the present invention will be apparent to those skilled in the art as the description proceeds.

To the accomplishment of the foregoing and related ends, our invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and annexed drawing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWING In the annexed drawing, FIG. 1 is a perspective view of the device of this invention mounted on the power switch of a power machine having an adjustable chuck;

FIG. 2 is an elevational cross-sectional frontal view of the safety device of FIG. I with its front cover removed; the power switch is in a power-off position with the slidable block raised to the lock position; and the chuck wrench is poised for insertion into the device to unlock it;

FIG. 3 is an elevational cross-sectional frontal view of the safety device of FIG. I with its front cover removed, the chuck wrench inserted into the device, and the slidable block lowered to the unlock position.

FIG. 4 is an elevational cross-sectional side view of the device taken along the line 44 of FIG. 2, its front cover and operating lever being shown in phantom.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now in greater detail to the drawing, the safety device 1 of the present invention is mounted on the faceplate of the power switch 2 of a power machine 3 and comprises a housing 4, generally square or rectangular in form having a front plate 5 providing a front face for the housing 4 and a rear plate 6 providing a backwall to the housing 4. The front plate 5 has an aperture 7 centered in its face. The front plate 5 is further provided with rearwardly directed upper, lower and side flange portions 8-11. The rear plate 6 of the housing 4 is similarly provided with a centered aperture 12 which is coaxially aligned with the central aperture 7 of front plate 5 and receives the tumbler 13 of the power switch 2 when the backplate 6 is bolted onto the power switch 2. The rear plate 6 is further provided with frontwardly extending upper and lower flanges 14 and 15. The front plate 5 and rear plate 6 fit together with the rearwardly directed upper and lower flanges 9 and 10 of front plate 5 overlaying the frontwardly directed upper and lower flanges l4 and 15 of rear plate 6; and the rearwardly directed side flanges 10 and ll of front plate 5 extend beyond the side edges of the rear plate 6, so that front and rear plates 5 and 6 form a substantially hollow chamber 16 for reception of the slidable block 17.

The slidable block 17 received in the housing 4 is generally rectangular with one corner cut away to form a sloping surface 18 preferably about 30 from horizontal. The block 17 is approximately of the same dimensions as the housing chamber 16 except that it is slightly shorter so that it is slidable in that chamber 16 along its vertical axis.

The block 17 is provided with an oblong tumbler receiving aperture 19 in its face substantially aligned with the tumbler receiving apertures 7 and 12 of the housing 4. The oblong tumbler receiving aperture 19 in the block 17 is elongated along its vertical axis.

The upper edge 20 of the slidable block 17 has a horizontal groove 21 extending along the entire surface of the block 17 between one edge and sloping cutaway corner surface 18.

Vertical bores 22 are provided in the bottom surface of the slidable block 17 and contain cylindrical helical springs 23 which rest on the floor of the housing 4 and urge the upper edge 20 of the block 17 upwardly against the upper end of the housing 4.

When the upper edge 20 of the block 17 actually rests against the upper end of the housing 4, the block 17 is in its socalled first or lock position as best shown in FIG. 2.

The side flanges and 11 of the front plate 5 are provided with circular apertures 24 and 25, respectively, in their upper ends. The apertures 24 and 25 are in horizontal alignment and the inclined surface 18 of the block 17 is located adjacent to and facing the aperture 24, hereinafter sometimes referred to as the ingress aperture 24.

When at rest in the first or lock" position, the inclined surface 18 of the block 17 protrudes into the generally cylindrical portion of the housing chamber 16 that is otherwise occupied by the cylindrical wrench handle 26 when received in the housing 4 (and protruding from both apertures 24 and 25 therein). When that cylindrical portion of the chamber 16 (hereinafter referred to as the wrench handle receptor zone or the adjuster tool receptor zone) receives the wrench handle 26, the tool makes initial contact with the inclined surface 18. When the tool is forced against that surface 18 in the horizontal direction, the block 17 is constrained against any substantial horizontal movement and responds by sliding downwardly against the upward urging of the springs 23 until the block 17 completely clears the tool receptor zone.

The block 17 clears the receptor zone at the same time as the wrench handle 26 reaches the end of the inclined surface 18 of the block 17, whereupon the handle 26 slides into the horizontal groove 21 on the upper edge of the block 17. Once the wrench handle 26 clears the sloping block surface 18, the entire upward thrust of the springs 23 is directed against the side of the wrench handle 26 and no component of this force tends to force the wrench handle 26 out of the housing 4. Accordingly, the block 17 is stabilized in this lower position (the so-called second or unlock position) at this point. Although the block 17 is stabilized, it is nevertheless preferable that the wrench handle 26 be inserted fully into the housing 4 so that it protrudes out of the opposite side from the egress aperture as best shown in FIG. 3.

In other embodiments of the present invention, the inclined block surface may run the entire length of the movable block s upper surface in which case the block would be stabilized in the second position only after pushing the adjuster tool entirely through the housing to protrude from the egress aperture 25. Or in a further embodiment, the egress aperture may be eliminated, the block being stabilized in the second position by a relatively long upper block surface running parallel to the longitudinal axis of the tool receptor zone, not unlike the grooved surface'32 shown in the drawings. Further embodiments may include other means to hold the movable block in its second position against the urging of the springs as will be apparent to persons of ordinary skill.

Returning to the detailed description of the device shown in the drawings, a power switch tumbler extension 27 is mounted on the power switch tumbler l3, and is provided with an enlarged cylindrical portion 28 and a coaxial narrow cylindrical portion 29. The enlarged portion 28 is provided with an axial aperture 30 receiving one end of the power switch tumbler 13 and a setscrew 31 rigidly affixes the extension 27 thereto. The enlarged portion 28 of the tumbler extension 27 locates in the housing chamber 16 and is received in the oblong aperture 19 of the movable block and the narrow cylindrical portion 29 extends out of the front of the housing 4 via the central housing apertures 7 and 12.

A locking pin 32 is rigidly mounted in the slidable block 17 with a setscrew 33 and extends vertically upwardly into the oblong block aperture 19. The enlarged cylindrical portion 28 of the tumbler extension 27 is provided with locking pin reception aperture which extends vertically upwardly so that it is coactially aligned with the locking pin 32 when the power switch 2 is in its power-off position.

Thus, when the power switch 2 is in its power-off position with the locking pin 32 of the slidable block 17 extending into the locking pin reception aperture 32 to interfere with rotation of the tumbler 13 the power switch 2 is locked in the power-off position.

When the wrench handle 26 is inserted through housing aperture 24 to force the block 17 downwardly to its second" position, the locking pin 32 moves downwardly out of the locking pin reception aperture 34 so that it is withdrawn from and no longer interferes with rotation of the tumbler 13 as shown in FIG. 3. Thus, when the wrench handle 26 holds the block 17 in its second position, the tumbler 13 can be rotated to turn on power in the power machine 3. So long as the wrench handle 26 remains in place, the machine 3 may be turned on and off without interference. Only after the wrench has been removed and the machine 3 turned off must the unlocking procedure be repeated.

An operating lever 35 is mounted on the tumbler extension 27 to facilitate rotation of the tumbler 13 between its poweron and power-off positions.

It will be appreciated that only objects of a particular size and shape will conveniently open or unlock the device 1 of the present invention. The object should at least be long enough to reach through the ingress aperture 24 and past the sloped block surface 18. In addition, the object must be wide enough to move the block a predetermined minimum distance from its first position to its second position in a direction divergent from and generally perpendicular to the longitudinal axis of the total receptor zone. The object must also not be wider than the ingress aperture 24. Inasmuch as it is relatively easy to calibrate both the distance which the movable block 17 must be moved to clear its locking pin 32 from the tumbler l3 and the diameter of the ingress aperture 24 to the diameter of the handle of the adjuster tool, the device may be set so that it cannot be conveniently unlocked with any object which is not substantially the same size and shape as one end of the adjuster tool itself. Accordingly, it is believed that it will generally be more convenient for the operator to use the adjuster tool itself than to find some other object to open the device and thereby defeat the purpose of the safety device.

In addition, while the device of the present invention may be installed as original equipment, it is also readily adaptable for mounting on a wide variety of different size power switches by merely altering the size or design of the power switch tumbler extension, thereby making the device highly suitable for secondary installation on used machinery. in certain instances, the power tumbler of the machine may be sufficiently long that no tumbler extension is required.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

Having thus described our invention, we claim:

1. A safety power switch locking device for adjustable power machinery utilizing a tool for making such adjustments, said device comprising:

a housing provided with a first aperture communicating with an adjuster tool receptor zone provided in said housing, said housing adapted for mounting on the power switch of the power machinery with a portion of the power switch tumbler projecting into said housing;

a movable member in said housing movable between a first position projecting into said adjuster tool receptor zone and a second position, said movable member spring biased toward said first position, said movable member movable from said first position to said second position under pressure exerted thereon by the adjuster tool inserted through said first aperture into said adjuster tool receptor zone;

a tumbler extension locating in said housing and adapted to mount on that portion of the power switch tumbler which projects into said housing when said housing is mounted on the power switch of the power machinery, a portion of said tumbler extension projecting out of said housing when so mounted, said tumbler extension provided with a slot; and,

a key disposed on said movable member projecting into said slot to prevent movement of said tumbler from its poweroff position to its power-on position when said movable member is in said first position, said key withdrawn from said slot when said movable member is in said second position.

2. A safety power switch locking device as recited in claim 1 wherein said adjuster tool fits in said first aperture with relatively close tolerance so that said movable member may not be pushed from said first position to said second position with objects which either are so wide as to not fit in said first aperture, or are so narrow as to not be sufficient to move said movable member far enough away from said tumbler extension to entirely withdraw said key therefrom. 

1. A safety power switch locking device for adjustable power machinery utilizing a tool for making such adjustments, said device comprising: a housing provided with a first aperture communicating with an adjuster tool receptor zone provided in said housing, said housing adapted for mounting on the power switch of the power machinery with a portion of the power switch tumbler projecting into said housing; a movable member in said housing movable between a first position projecting into said adjuster tool receptor zone and a second position, said movable member spring biased toward said first position, said movable member movable from said first position to said second position under pressure exerted thereon by the adjuster tool inserted through said first aperture into said adjuster tool receptor zone; a tumbler extension locating in said housing and adapted to mount on that portion of the power switch tumbler which projects into said housing when said housing is mounted on the power switch of the power machinery, a portion of said tumbler extension projecting out of said housing when so mounted, said tumbler extension provided with a slot; and, a key disposed on said movable member projecting into said slot to prevent movement of said tumbler from its power-off position to its power-on position when said movable member is in said first position, said key withdrawn from said slot when said movable member is in said second position.
 2. A safety power switch locking device as recited in claim 1 wherein said adjuster tool fits in said first aperture with relatively close tolerance so that said movable member may not be pushed from said first position to said second position with objects which either are so wide as to not fit in said first aperture, or are so narrow as to not be sufficient to move said movable member far enough away from said tumbler extension to entirely withdraw said key therefrom. 